common mistakes by DBA

Listing down common mistakes that every DBA makes at least once in his career , there are few which are common for beginner but more often for "good experienced DBA's" too.

Here i highlighted experience DBA's are always good ,even though they make mistake but keeps courage to recover and learn from it :)

1 : Attempt to start the DB which is already running !

yeah ! i knew it you have done that , so even i.

This mostly happens during planned activity , OS admin asked to startup DB but its already up through cluster through init services.